Believe great majority of people to tap water often "reveal" the peculiar smell will not be strange, actually this is the performance that water purification process USES liquid chlorine to disinfect.

The taste remains in tap water because some of the chlorine is still in the water, a sign that drinking water has been treated with chlorine.

This raises questions about whether chlorine-treated drinking water is really safe and non-toxic.

This requires understanding the following two questions.

◎ How does chlorine disinfect water?

◎ whether the method of chloride will produce toxic side products, thus harmful to human health?

When chlorine comes into contact with water, it generally produces a "disproportionation reaction" to form hypochlorous acid and hydrochloric acid.

The sterilizing ingredient is hypochlorous acid, a small, neutral molecule that first spreads to the surface of negatively charged bacteria and then USES its strong penetration to penetrate directly into the cell wall.

Chlorine kills bacteria by destroying their enzyme system.

As early as the early 20th century, chlorination was widely used in water disinfection.

As technology advances, however, so do the problems of chlorinating drinking water.

As early as 1974, scientists discovered harmful "toxic byproducts" in chlorinated tap water.

Originally, in the process of chlorine and water action, chlorine also had a chemical action with the residual organic matter in the water at the same time, a lot of toxic compounds such as chloroform (namely chloroform), bromoform, bromodichloromethane, chlorodibromomethane and other substances were also produced.

Two years later, the national cancer society found scientific evidence of a causal link between chloroform and cancer in animals.

By the 1990s, epidemiologists had found a potential correlation between the incidence of diseases such as bladder, rectal and colon cancer and the amount of chlorine disinfectant consumed.

However, in view of the advantages of chlorination in water disinfection, it is still widely used, in the case of large amount of water, the treatment cost of chlorination is lower;

Second, because the water can maintain a certain amount of residual chlorine for a long time after chlorine disinfection, the continuous disinfection ability is strong;

Third, chlorine disinfection has been a relatively mature disinfection method.

At the same time, people did not turn a blind eye to the toxic by-products produced in the water after chlorine disinfection.

In order to control these by-products of drinking water disinfection, countries have introduced strict standards.

In 1975, the United States set the upper limit of trichloromethane concentration at 100 micrograms per liter and planned to reduce it to 40 micrograms per liter in stages.

In 1985, the highest concentration of trichloromethane was set as 60 micrograms per liter in the sanitary standard for drinking water in China.

However, we should be aware of the fact that the substances involved in the standard are toxic substances that have been thoroughly studied, and many toxic by-products that have not been detected or taken seriously are not included in the standard.

In the "drinking water quality guidelines" formulated by the world health organization in 1984, there are as many as 23 disinfection byproducts of chlorine treatment alone, and the assessment index of the above standard only trichloromethane.

In the face of the worsening water environment, it is reasonable to believe that trichloromethane is only a small part of the toxic by-products of chlorine treatment.

However, at present, we do not have the conditions to abandon chlorine disinfection.

When it comes to the safety of drinking water, it is necessary to ensure that the effects of microorganisms on human health are eliminated before the harm of disinfection by-products to human body can be reduced.

The most vivid example of this problem occurred in Peru in 1991.

At that time, cholera, which had been extinct for many years, resumed its ravages in Peru, even in neighboring countries.

Public health experts say the phenomenon is linked to local efforts to disinfect water because of concerns that the by-products of chlorine disinfection could cause cancer.

At present, scientists from all over the world are working to develop a safe and effective drinking water treatment technology to protect human beings from toxic by-products.

Scientists have tried many ways to clean water, such as ultraviolet disinfection and ozone-treated water, but they have been either too expensive or not very effective.

So the history of drinking chlorine-treated tap water will continue for some time.